1. Field of the Invention
The present invention relates to cellulase variants capable of removing soil from fabric, a detergent composition comprising the cellulase variants, a method of washing a soiled fabric with the cellulase variants, and use of the cellulase variants e.g. in detergent compositions, in fabric softeners, for color clarification of textile fabrics (removal of fluffs and pills), for preventing backstaining in washing of fabric, for soil removal, for deinking of used paper, and for pulp recycling.
2. Description of the Related Art
Repeated washing of fabrics, especially cellulose containing fabrics, generally causes a harsh texture in the fabric used. To remedy this problem the use of cellulases, i.e. cellulolytic enzymes, for harshness reduction of cellulose containing fabrics, e.g. cotton, was suggested and demonstrated previously.
The practical exploitation of cellulases has, to some extent, been hindered by the nature of the known cellulase preparations. These known preparations are often complex mixtures of a variety of single cellulase components, and which may have a rather low specific activity. It is difficult to optimize the production of single components in multiple enzyme systems and thus to implement industrial cost-effective production of cellulases, and their actual use has been hampered by difficulties arising from the need to employ rather large quantities of the enzymes to achieve the desired effect.
The drawbacks of previously suggested cellulases may be remedied by using single-component enzymes selected for a high specific activity. Single-component cellulases are described in, e.g. WO 91/17243, WO 91/17244 and WO 91/10732.
For example, WO 91/17244 discloses a cellulose-degrading enzyme (a cellulase) derivable from a fungus other than Trichoderma or Phanerochaete which comprises a carbohydrate binding domain homologous to a terminal A region of Trichoderma reesei cellulases, the carbohydrate binding domain being capable of effecting binding of the enzyme to an insoluble cellulosic substrate, which may be employed for textile treatment, e.g. for reducing the harshness of cotton-containing fabrics and for soil removal and color clarification of fabrics. Example 3 and FIG. 13 disclose the preparation of a Fusarium oxysporum C-family endoglucanase and the DNA sequence and derived amino acid sequence thereof, respectively. Later it was found that the disclosed amino acid sequence was not correct; the corrected sequence is published in Sheppard, P. O., Grant, F. J., Oort, P. J., Sprecher, C. A., Foster, D. C., Hagen, F. S., Upshall, A., Mcknight, G. L. and Ohara, P. J.: The use of conserved cellulase family-specific sequences to clone cellulase homolog cDNAs from Fusarium oxysporum. Gene 150:163-167, 1994. Example 4 and FIGS. 14A-E discloses the preparation of a Humicola insolens endoglucanase 1 (EG I) and the DNA sequence and derived amino acid sequence thereof, respectively. Further, in example 4 (page 32, line 1 to 5) is described the construction of expression plasmid of a truncated EG I (denoted EG I') wherein the last 13 amino acids of the coding region were eliminated and the altering of Val to Leu in position 421 (position 401 in the sequence of the enzyme). The gist of the invention disclosed in WO 91/17244 is to provide a cellulase which, besides the enzyme core, has a carbohydrate binding domain (CBD) which is homologous to the A region of Trichoderma reesei cellulases, since the function of the CBD in the enzyme molecule was believed to be to mediate binding to solid substrates including cellulose and consequently to enhance the activity of such enzymes towards such substrates.
The present invention seeks to address the drawbacks of previously suggested cellulases and is directed to single-component endoglucanases having enhanced enzyme activity in the alkaline pH range, while at the same time exerting a moderate cellulolytic action on the cellulosic substrate. In other words, the endoglucanase should neither destroy the cellulosic substrate as such. For example, when the substrate is a cellulosic fabric, the used endoglucanase should not result in a substantial tensile strength loss of the fabric. The enhanced alkaline activity of the enzyme is also essential, since most applications of endoglucanases advantageously take place in the alkaline pH range.